PROJECT SUMMARY AND ABSTRACT Recent outbreaks of Zika virus (ZIKV) in Polynesia and Brazil correlate with adverse neurological disorders ? fetal microcephaly and Guillain-Barr syndrome ? prompting the World Health Organization to declare this virus a public health emergency of international concern. No therapy is currently available to treat ZIKV infection, and it follows that there is an urgent need for readily available and safe treatment options. We discovered a FDA-approved drug (code SSZ) that inhibits ZIKV infection in Vero cells (a monkey kidney line devoid of interferon signaling) and primary placental Hofbauer cells. SSZ is approved for the treatment of arthritis and digestive disorders with a well-established safety profile. Importantly, SSZ is a category B pregnancy drug as high-dose studies in pregnant rats and rabbits did not cause abnormal fetal development. This proposal seeks to further evaluate SSZ as a safe pre-clinical candidate for ZIKV treatment alone and in combination with other active agents. Two aims are proposed in this application to be pursued in parallel with on-going animal studies in Brazil. Aim 1 is to profile the antiviral activity of SSZ in pre-clinical and translational studies. The first aim will investigate SSZ inhibition and safety in primary cells permissive to ZIKV infection. The lines to be evaluated are listed, but not limited to, cells at the site of infection (fibroblasts, keratinocytes and dendritic cells) and the central nervous system (neuroblasts). Additionally, inhibition kinetics will be assessed to model potential treatment modalities en route to clinical trials. These results will support and parallel on-going animal studies with collaborators in endemic countries. SSZ will be further evaluated in combination studies with other FDA-approved drugs that were recently found to possess anti-ZIKV activity. Aim 2 seeks to determine if SSZ primarily inhibits ZIKV directly through viral proteins or indirectly through host immune rescue. The viral non-structural protein 5 (NS5) responsible for viral RNA replication and processing and antagonizing host immune response, and preliminary data suggests that SSZ binds to ZIKV NS5. SSZ may act as a non-nucleotide NS5 inhibitor while also rescuing host immune response ? a dual host/pathogen mechanism of action. The aims outlined in this project hold promise to identify a novel mechanism of antiviral action towards repurposing a safe FDA-approved drug in rapid response to the on-going ZIKV outbreak.